It is well known to treat various oil refinery charge stocks to extract improved fuel values therefrom or to convert them to valuable petrochemicals. A major problem encountered in the treatment of various hydrocarbon charge stocks is the phenomenon recognized and descriptively called fouling. This phenomenon is manifested in the form of deposits which frequently form on the metal surfaces of the processing equipment and tend to naturally decrease the efficiency of the intermediate processing operations. The results of fouling appear in the form of heat transfer loss, pressure drop, loss in throughput rate and an increase in corrosion of the equipment.
The charge stocks which most commonly cause fouling in intermediate refinery equipment are naphthas, gas oils, crude, and petroleum gases. The naphthas or light distillates may be considered as a light oil usually having a boiling point range of 32.degree.-260.degree. C. The gas oils are intermediates between the so-called kerosene fractions and the light lubricating oils, and generally distill in the range of 260.degree.-540.degree. C. Those gas oils are usually used as charges to cracking units where the molecules are broken down into smaller components. The crude oils which most often cause the problem of fouling are charged to the first refining stage operations and contain all the petroleum fractions normally removed in the refining processes. Crude stocks include the residual fraction which remain after the more valuable components and solvent extractable components of the crudes have been removed.
Another class of hydrocarbons where fouling problems arise and which are ameliorated by the method of the present invention is the petroleum gases or normally gaseous alkane and alkene hydrocarbons which normally boil in the range of -250.degree. to 100.degree. C., i.e., methane, ethane, propane, butane, ethylene, propylene, etc. These hydrocarbons may be in the liquefied state or gaseous state during processing thereof in the practice of the method of the present invention.
The various charge stocks mentioned above are most frequently subjected to one or more of the following general type thermal or catalytic processes to produce fuel: fractionation, reforming, cracking, alkylation, isomerization, polymerization, desulfurization, hydrogenation and dehydrogenation.
Similar fouling problems arise in equipment used in the petrochemical industry wherein the hydrocarbon charge stock is, in most cases, heated at normal or elevated temperatures and pressures. For example, acetylene may be produced from light naphtha or natural gas. Ammonia may be produced by mixing a compressed hydrocarbon gas, liquid hydrocarbon or the like with steam. Benzene and hydrogen are reacted to produce cyclohexane. Light alkane hydrocarbons may be used to produce mono-olefins and di-olefins. Ethylene fuel may be heated under pressure to produce ethanol. Light and heavy crude oils, as well as light hydrocarbon gases may be thermally cracked into ethylene, propylene, and C.sub.4 olefins.
The foregoing examples of petrochemical processes are illustrations but not exhaustive of processes where fouling problems arise such that the practice of the method of the present invention may be used advantageously.
It is common practice to add chemical agents to the above-mentioned fuel stocks to reduce the fouling of the processing equipment. One known antifoulant is the Mannich condensation product of an alkylphenol, an aldehyde, and an amine.
U.S. Pat. No. 4,166,726 suggests the use of such condensation product as diesel fuel additives to provide improved combustion of such fuel.
U.S. Pat. No. 4,810,354 discloses a method of inhibiting fouling in hydrocarbon processing equipment by using an effective amount of the Mannich condensation product of an alkoxylated alkylphenol, an aldehyde and a polyamine.
It has been found that even with the use of the aforementioned Mannich condensation products, undesirable fouling occurs during the thermal processing of hydrocarbon stocks.
The present invention provides a process for substantially reducing the fouling normally experienced in processing petroleum hydrocarbon liquids at elevated temperatures. Thus, the practice of the present invention inhibits the build-up of deposits in processing equipment that would otherwise reduce throughput capacity.